Enhanced ratio control to establish CVT ratio with excellent precision

ABSTRACT

A system for enhanced ratio control in a continuously variable transmission (CVT) includes a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT. At least one sensor generates a train of pulses indicative of speed of rotation of a predetermined rotary member of the CVT. A measured CVT ratio generator derives information of an actual CVT ratio out of at least the train of pulses to give a measured value of CVT ratio. A filter processes the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio. A command generator determines the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone. A filter and command generator manager narrows the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished and adjusts filter gain at the filter in a manner to keep amplitude at frequency of noise that is contained in the measured value of CVT ratio within the narrowed dead zone.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and a system forenhanced ratio control in a continuously variable transmission.

[0003] 2. Description of the Background Art

[0004] Continuously variable transmissions (CVT's) are transmissionsthat change a speed ratio continuously, not in discrete intervals. Thiscontinuous nature of CVT's gives them an infinite number of speedratios, making them very attractive for automotive use.

[0005] Various types of CVT are known. One such example is a CVT withpulley/V-belt power transfer. Another example is a CVT with disc/rollerpower transfer. The CVT of this type is often referred to as atoroidal-type CVT (TCVT) because it transmits torque from one rotatingsemi-toroidal disc to another semi-toroidal disc by traction rollersthrough a traction force. The two semi-toroidal discs form a toroidalcavity. In each toroidal cavity, it is preferred to have two tractionrollers in equiangularly spaced relationship engaging the discs fortransmission of motion therebetween. While three or four tractionrollers may be disposed in spaced relationship in each toroidal cavityand will provide increased life for contact surfaces as the totalsurface area is increased, two traction rollers are preferred forsimplicity.

[0006] Each traction roller is rotatably supported by a pivot trunnion,respectively. The pivot trunnions, in turn, are supported to pivot abouttheir respective pivot axis. In order to controllably pivot the pivottrunnions for a ratio change, a hydraulic control means is provided. Thehydraulic control means is included in a hydraulic cylinder at eachpivot trunnion and includes a control volume defined in the hydrauliccylinder between a piston and an axial end of the hydraulic cylinder.The pistons within the hydraulic cylinders are connected to the pivottrunnions along their pivot axis by rods. The piston and its associatedrod are thereby rotatable about the pivot axis with the associated pivottrunnion. Variation of the control volume causes the piston to moverelative to the hydraulic cylinder, and applies a control force todisplace the pivot trunnions. Control forces applied displace the pivottrunnions in the opposite directions along their pivot axis. As aresult, the pivot trunnions are caused to pivot about their respectivepivot axis, due to the forces present in the rotating toroidal discs,for initiating ratio change.

[0007] For terminating the ratio change when a desired ratio has beenobtained, a feedback structure is provided. The feedback structurepreferably includes a source of hydraulic pressure, and a ratio controlvalve for controlling the flow of hydraulic fluid for initiating ratiochange. The feedback structure further includes a mechanism associatedwith at least one pivot trunnion to adjust the ratio control valve uponpivotal movement of the pivot trunnion to a desired ratio. The mechanismis preferably a cam connected to a pivot trunnion. The cam may be linkedmechanically and/or electronically to operate the ratio control valveupon reaching a desired rotation.

[0008] In CVTs, a measured value of CVT involves noise, which may causehunting in CVT ratio. Suppression of such hunting is proposed by JP-A8-277927.

[0009] According to this known technique, a dead zone is provided. Thewidth of dead zone is variable in response to revolution speed of CVTinput or output member or the product of revolution speeds of CVT inputand output members. The dead zone is compared to a deviation between adesired value of CVT ratio and a measured value of CVT ratio. When thedeviation falls in the dead zone, a ratio change is suspended. Themeasured value of CVT ratio inevitably involves noise because trains ofoutput pulses of revolution speed sensors are used in calculating aratio between a revolution speed of a CVT input member and a revolutionspeed of a CVT output member.

[0010] This section is a description on noise inevitably included in ameasured value of CVT ratio. Each unit of CVT uses revolution speedsensors, each of which includes a toothed wheel coupled to an input oroutput shaft, and a Hall element sensor. The sensors generate trains ofpulses. A filter is provided to deal with noise contained in themeasured value of CVT ratio. Due to product-by-product variability inprocessing accuracy of toothed wheels, the width of noise afterfiltering may differ from one unit to another. This noise problem hasnot been solved by the prior art because the width of a dead zone iscontrolled in an open loop manner. The width of the dead zone isdifficult to nicely fit all noise situations derived from difference inthe width of noise from one unit to another. To clearly illustrate thisdifficulty, FIGS. 26A, 26B and 26C have been prepared to consider, twocases, namely case 1 and case 2. FIG. 26A shows typical pattern of noiseafter filtering and dead zones of cases 1 and 2. As shown in FIG. 26A,the width of dead zone of case 1 is narrower than the width of dead zoneof case 2. FIG. 26B illustrates a problem inherent with the case 1,while FIG. 26C illustrates a problem inherent with the case 2. As shownin FIG. 26B, the dead zone is exceeded, causing hunting of actuatorcommand that leads to undesired pulsating ratio change. As shown in FIG.26C, there remains a standing deviation from a desired value of CVTratio.

[0011] A need remains for improving the conventional CVT ratio controlto remove at least one of the following insufficiencies.

[0012] a) Due to hunting or standing wave, a CVT cannot alwaysestablish, with good precision, a predetermined value of CVT ratiorequired for moving the vehicle from standstill. In this case, thedriver feels unpleasantly a difference in vehicle acceleration uponstarting the vehicle. This predetermined value of CVT ratio iscomparable to the lowest gear ratio in the conventional discrete typetransmission.

[0013] b) Due to difficulty in establishing, with good precision, adesired value of CVT ratio, a usable range of CVT ratios is narrowed toleave a relatively wide margin at each of mechanical limits asillustrated in FIG. 27. Fuel economy may be improved by extending theusable range of CVT ratios sufficiently to provide a wide range of CVTratios for fuel efficient operation with CVT ratios at high vehiclespeeds. However, so extending the usable range of CVT ratios requires anincrease in size of a CVT unit to provide the margins, pushing upmanufacturing cost. If such increase in size of a CVT unit is notdesired, one cannot accomplish an improvement in fuel economy as high asexpected.

[0014] c) Difficulty in establishing, with good precision, a desiredvalue of CVT ratio makes it difficult for an infinitely variabletransmission (IVT) to have a geared neutral point (GNP). The IVTincludes a CVT in combination with a constant ratio transmission and aplanetary gearing mechanism. The GNP is a point at which an infinitelygreat ratio is established to provide zero driving force.

[0015] An object of the present invention is to provide a method andsystem for enhanced CVT control with intelligent noise management toaccomplish a desired CVT ratio with excellent precision without huntingand standing deviation.

SUMMARY OF THE INVENTION

[0016] According to one aspect of the present invention, there isprovided system for enhanced ratio control in a continuously variabletransmission (CVT) including a ratio control element positionable by anactuator in response to an actuator command to establish various CVTratios in the CVT, the system comprising:

[0017] a measured CVT ratio generator obtaining information of an actualCVT ratio established in the CVT to give a measured value of CVT ratio;

[0018] a filter processing the measured value of CVT ratio in a mannerto refine the information of the actual CVT ratio to give an estimatedvalue of CVT ratio;

[0019] a command generator determining the actuator command such thatthe actuator command remains unaltered when a deviation of the estimatedvalue of CVT ratio from a desired value of CVT ratio stays within a deadzone; and

[0020] a filter and command generator manager narrowing the dead zone tomeet precision requirement upon determination that the desired value ofCVT ratio has been accomplished and adjusting the filter to gainrequirement for keeping the magnitude of signal at frequency of noisewithin the narrowed dead zone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will be apparent from reading of the followingdescription in conjunction with the accompanying drawings.

[0022]FIG. 1 is a schematic top view of a continuously variabletransmission (CVT) including a dual cavity toroidal drive, a planetarydrive, and a hydraulic drive.

[0023]FIG. 2 is a schematic side view of a pair of traction rollerassemblies disposed in the rearward cavity of the toroidal drive of FIG.1 and a schematic representation of a pressure control for a tractiondrive.

[0024]FIG. 3 is a block diagram showing the relationship between a CVTcontroller and an actuator.

[0025]FIG. 4 is a control diagram of a CVT controller according to thepresent invention.

[0026]FIG. 5 is a portion of a control diagram of a CVT controller usinga low pass filter.

[0027]FIG. 6 is a gain vs., frequency characteristic of the low passfilter.

[0028]FIG. 7 is a portion of a control diagram of a CVT controller usingan estimator as a filter.

[0029]FIG. 8 is a low pass filter characteristic of the estimator from ameasured value of trunnion angular position to an estimated value oftrunnion angular position.

[0030]FIG. 9 is a conversion table between trunnion angular position andCVT ratio used to convert a measured value of CVT ratio to a measuredvalue of trunnion angular position and to convert an estimated value oftrunnion angular position to an estimated value of CVT ratio.

[0031]FIG. 10 is a portion of a control diagram of a CVT controllerusing a band reject filter.

[0032]FIG. 11 is amplitude vs., frequency characteristic of noisecontained in a measured value of CVT ratio.

[0033]FIG. 12 is a gain vs., frequency characteristic of the band rejectfilter designed for eliminating noise shown in FIG. 10.

[0034]FIG. 13 is a shift map.

[0035]FIG. 14 is a look-up table illustrating various CVT ratiointervals determined by resolution of an actuator in the form of astepper motor at different CVT ratios.

[0036]FIG. 15 is a control diagram of a command generator of a CVTcontroller.

[0037]FIG. 16 is a control diagram of another command generator of a CVTcontroller.

[0038]FIG. 17 is a flow chart of a control routine implementing thepresent invention.

[0039]FIG. 18 is a flow chart of a sub-routine.

[0040]FIG. 19 is a flow chart of a sub-routine.

[0041]FIG. 20 is a simulation result confirming the effectiveness of thepresent invention.

[0042]FIG. 21 is a schematic diagram a CVT including a dual cavitytoroidal drive and a planetary gearing to form an infinitely variabletransmission (IVT).

[0043]FIG. 22 is a map illustrating a direct mode and a powerrecirculation mode.

[0044]FIG. 23 is a diagram illustrating a case 1 wherein the width ofdead zone about a desired value of CVT ratio is narrower than aninterval ΔG between the two adjacent values of CVT ratio as well as acase 2 wherein the width of dead zone is wider than the interval ΔG.

[0045]FIGS. 24A, 24B and 24C are simulation results showing theeffectiveness of an embodiment according to the present invention ascompared to two comparative examples.

[0046]FIG. 25 is graphical representation showing the relationshipbetween control gain and dead zone.

[0047]FIGS. 26A, 26B and 26C illustrate two excessive cases in settingdead zone.

[0048]FIG. 27 is a diagram illustrating a conventional setting of arange of CVT ratios.

DESCRIPTION OF THE EMBODIMENTS

[0049] Referring to FIGS. 1 and 2, a CVT 10 includes a dual cavitytoroidal drive 12 coaxially connected to a forward positioned input gearsection 14 and connected also to a rearward positioned output gearsection 16. For purpose of clarification, the terms front or forwardrefer to the right side, and rear or rearward refer to the left side ofthe view shown in FIG. 1. All three elements 12, 14 and 16 are enclosedin a housing 18 and driven by an input or turbine shaft 20 that ispowered by an engine (not shown) through a torque converter 22 or alock-up clutch 24. Housing 18 has three chambers, one for each element12 ,14 and 16, separated by walls 26 and 28. Torque converter 22 is aconventional torque converter including a pump impeller 30 connected tothe engine, a turbine runner 32 connected to input shaft 20, and astator 34 grounded via a one-way brake 36. Lock-up clutch 24 is aconventional lock-up clutch including a clutch element 38 connected toinput shaft 20.

[0050] Dual cavity toroidal drive 12 includes first and second outboardtraction discs 40 and 42 mounted on a torque sleeve 44 via ball splines46 and 48 to rotate in unison. Toroidal drive 12 further includes twoinboard traction discs 50 and 52, which are positioned back-to-back androtatably mounted on sleeve 44, and both coupled to an output gear 54 torotate in unison. Two inboard traction discs 50 and 52 may be formed asone integral element formed with output gear 54. In this case, theintegral element is a dual-faced single disc element rotatably supportedby sleeve 44. One example of a dual cavity toroidal drive having dualinboard discs positioned back-to-back is disclosed in U.S. Pat. No.5,902,208 issued May 11, 1999 to Nakano, which is incorporated in itsentirety herein by reference. Another example of a dual cavity toroidaldrive having a dual-faced single disc element formed with an output gearis disclosed in co-pending U.S. patent application Ser. No. 09/940,875commonly assigned herewith, which is incorporated in its entirety hereinby reference. This incorporated U.S. patent application Ser. No.09/940,875 has the corresponding European Patent Application publishedunder EP 1 186 798 A2 on Mar. 13, 2002. A toroidal cavity is definedbetween each outboard discs 40 and 42 and one of the inboard discs 50and 52. A pair of motion transmitting traction rollers 56, 58, 60 and 62is disposed in each toroidal cavity, with one roller being disposedtransversely on either side of each cavity (see FIGS. 1 and 2). Eachpair of traction rollers 56, 58, 60 and 62 is a mirror image of theother pair. Therefore, only the one pair of rollers 60 and 62 isillustrated in FIG. 2. Each pair of traction rollers 56, 58, 60 and 62are engaged between each outboard discs 40 and 42 and one of the inboarddiscs 50 and 52 in circles of varying diameters depending on thetransmission ratio. Traction rollers 56, 58, 60 and 62 are so supportivethat they can be moved to initiate a change in the ratio. That is, eachroller 56, 58, 60 and 62 can be actuated to vary its diameter andprovide a substantial normal force at their points of contact with thecorresponding discs to sufficiently support the traction forces neededto effect the change in ratio. With outboard discs 40 and 42 beingrotated continuously by the engine, outboard discs 40 and 42 impinge ontraction rollers 56, 58, 60 and 62, causing the traction rollers torotate. As they rotate, the traction rollers impinge on and rotateinboard discs 50 and 52 in a direction opposite to that of rotatingoutboard discs 40 and 42. The structure and operation of the otherelements of the toroidal drive 12 will be discussed later on in thespecification.

[0051] With continuing reference to FIG. 1, toroidal drive 12 employs acam loading system to control normal force between toroidal discs (50,52, 60, 62) and traction rollers (56, 58, 60, 62). The cam loadingsystem operates on outboard discs 40 and 42 to apply an axial force thatis a linear function of the input torque. Describing, in detail, the camloading system, torque sleeve 44 extends beyond the backs of outboarddiscs 40 and 42 and has flanges (not shown) at its front and rear endsto carry thrust bearings 64 and 66. The cam loading system includes adisc spring (Belleville spring) 68, which is supported on torque sleeve44 between thrust bearing 66 and the back of toroidal disc 42 to operateon the disc. The cam loading system also includes a drive plate 70rotatably supported by torque sleeve 44 via thrust bearing 64. The camloading system further includes cam rollers 72, which are disposedbetween drive plate 70 and toroidal disc 40. An example of a cam loadingsystem having cam rollers between a drive plate and one of outboardtoroidal discs is disclosed in U.S. Pat. No. 5,027,668 issued Jul. 2,1991 to Nakano, which is incorporated in its entirety herein byreference.

[0052] Drive plate 70 of the cam loading system is drivingly connectedto input shaft 20 through input gear section 14. Input gear section 14includes a dual-pinion planetary gear system (DPGS) 74, a forward clutch76, and a reverse brake 78. DPGS 74 includes, in a conventional manner,a sun gear 80, a carrier 82, a ring gear 84, and a plurality of pairs ofintermeshed planet pinions 86 and 88 rotatably supported by pins ofcarrier 82. Pinions 86 and 88 are disposed between sun and ring gears 80and 84, with inner pinions 86 in engagement with sun gear 80 and outerpinions 88 in engagement with ring gear 84. Sun gear 80 is coupled withinput shaft 20 to rotate in unison. Carrier 82 is connected to driveplate 70 of the cam loading system for rotation in unison. Carrier 82 isconnectable to input shaft 20 through forward clutch 76. Ring gear 84 isconnectable to housing 18 through reverse brake 78.

[0053] Input gear section 14 including DPGS 74 functions to establishtorque transmission in forward drive mode or reverse drive mode. In theforward drive mode, forward clutch 76 is engaged with reverse brake 78released. In the reverse drive mode, reverse brake 78 is applied withforward clutch 76 disengaged. In this manner, input torque is applied todrive plate 70 to continuously rotate outboard toroidal discs 40 and 42in the same direction as that of input shaft 20 in the forward drivemode, but in a direction opposite to that of input shaft 20 in thereverse drive mode. The input torque is transmitted from outboard discs40 and 42 to inboard discs 50 and 52 to rotate output gear 54.

[0054] Output gear section 16 including an input gear 90 of a countershaft 92 functions to provide torque transmission from output gear 54.Output gear 54 is in engagement with input gear 90 of counter shaft 92,which has an output gear 94. Output gear section 16 also includes a gear96 of an output shaft 98. Output gear section 16 may include an idlergear (not shown) between output gear 94 and gear 96. Rotation of inboardtoroidal discs 50 and 52 is transmitted via output gear 54, gear 90,counter shaft 92, gear 94 and gear 96 to output shaft 98.

[0055] Referring to FIG. 2, toroidal drive 12 in this embodimentincludes two traction rollers 60, 62 in each toroidal cavity. Each ofthe rollers 60, 62 is rotatably supported by a pivot trunnion 100, 102,respectively. Pivot trunnions 100, 102, in turn, are supported to pivotabout their respective pivot axis 104, 106. Each of traction rollers 60,62 and the corresponding pivot trunnion 100, 102 are components oftraction roller assemblies 108, 110.

[0056] As is well known to those skilled in the art, the surfaces oftoroidal discs 40, 42, 50, 52 defining cavities have a radius ofcurvature, the origin of which coincides with the pivot axis 104, 106.This geometry permits the pivot trunnions and traction rollers to pivotand maintain contact with the surfaces of the toroidal discs.

[0057] Traction roller assemblies 108, 110 each also include a hydraulicpiston assembly 112, 114 in addition to the pivot trunnion 100, 102.Pivot trunnions 100, 102 each have a backing plate 116, 118 thatsupports traction roller 60, 62 rotatably. Bearings 120, 122, positionedbetween plate 116, 118 and traction roller 60, 62, permit relativerotation between backing plate 116, 118 and traction roller 60, 62.Backing plates 116, 118 each have an extension 124, 126 that supportstraction roller 60, 62, on a bearing not shown, for rotation.

[0058] Hydraulic piston assembly 112, 114 includes a housing 128, 130enclosing a cylinder 132, 134 in which is slidably disposed a piston androd 136, 138. Piston and rod 136, 138 divides cylinder 132, 134 intoequal area chambers including a first chamber 140, 142 and a secondchamber 144, 146. Piston and rod 136, 138 is disposed so that itscenterline 148, 150 is disposed substantially along pivot axis 104, 106,respectively. So positioned, piston and rod 136, 138 is able to pivotabout pivot axis 104, 106 with pivot trunnion 100, 102, respectively.

[0059] The pressure in first and second chambers 140, 142; 144, 146 areestablished by a hydraulic control system 152. Hydraulic control system152 includes a pump, not shown, an electro-hydraulic control 154, aratio control valve 156, and a feedback structure 158. The pump is aconventional pump that draws hydraulic fluid from a reservoir 160 anddelivers the fluid to electro-hydraulic control 154 from which the fluidis delivered to ratio control valve 156.

[0060] Control 154 delivers system (or line) pressure Pl to a passage162 that is connected to an inlet port 164 of ratio control valve 156.Ratio control valve 156 has a spool 166 slidably disposed in a valvebore 168. Valve bore 168 is in fluid communication with passage 162 viainlet port 164. Valve bore 168 is also in fluid communication with afirst control passage 170 via a first control port 172, and with asecond control passage 174 via a second control port 176. Valve bore 168is further in fluid communication with a first drain passage 178 via afirst drain port 180, and with a second drain passage 182 via a seconddrain port 184.

[0061] Spool 166 is connected to a feedback lever 186, which is acomponent of feedback structure 158. A ratio actuator 188, in the formof a stepper motor, for example, receives a control signal. The controlsignal is an actuator command indicative of motor steps if a steppermotor is used as the actuator. In response to the control signal,actuator 188 moves feedback lever 186, connected to an actuator shaft190, to initiate the ratio change in toroidal drive 12. Feedback lever186 is connected to actuator shaft 190 at one end and to a bell crank192 at the other end. At a point between the two ends, the feedbacklever 186 is pivotally connected to a spool rod 194, which is connectedto spool 166 to move in unison. Bell crank 192 has one end 196 pivotallyconnected to the other end of feedback lever 186 and the other end 198.The other end 198 of bell crank 192 is controlled by the angularposition about pivot axis 104 of traction roller assembly 108 throughcontact with a cam 200 formed on piston and rod 136. As actuator 188moves feedback lever 186, valve 156 alters, in response to movement ofvalve rod 194, the hydraulic pressure in lines 170 and 174. Hydraulicpressure is provided to the valve 156 through line 162, which issupplied with system or line pressure. As the pressure in lines 170 and174 is altered, traction roller assemblies 108 and 110 move along pivotaxis 104 and 106 in the opposite directions and then pivot about pivotaxis 104 and 106, changing the ratio in toroidal drive 12. As tractionroller assembly 108 pivots, lever 186 moves, due to rotation of cam 200and movement of bell crank 192, repositioning valve rod 194, providingmeans for valve 156 to reinstate the pressure in lines 170 and 174 tostop traction roller assemblies 108 and 110 from pivoting.

[0062] Actuator 188 controls displacement of actuator shaft 190, which,in turn, controls the ratio in toroidal drive 12. If actuator 188 is inthe form of a stepper motor, as is in exemplary embodiments of thepresent invention, controlling angular displacement of stepper motor interms of motor steps controls the ratio in toroidal drive 12.

[0063] In the embodiment shown in FIG. 1, an input speed sensor 202detects the speed of rotation of the input shaft 20, and an output speedsensor 204 detects the speed of rotation of the output shaft 98. Theoutput of the sensor 202 may be used in deriving information of thespeed of rotation of the outboard disc 40, which may be called an inputdisc. The output of the sensor 204 may be used in deriving informationof the speed of rotation of the inboard disc 50, which may be called anoutput disc.

[0064] With reference now to FIG. 3, in an exemplary embodiment of thepresent invention, a CVT controller 300 comprises a microprocessor-basedcontroller with an associated microprocessor, represented by amicroprocessor 302. The microprocessor 302 communicates with associatedcomputer-readable storage media 304. As will be appreciated by one ofordinary skilled in the art, the computer-readable storage media 304 mayinclude various devices for storing data representing instructionsexecutable by the microprocessor to control the TCVT 10. For example,the computer-readable storage media 304 may include a random accessmemory (RAM) 306, a read-only memory (ROM) 308, and/or a keep-alivememory (KAM) 310. These functions may be carried out through any of anumber of known physical devices including EPROM, EEPROM, flash memory,and the like. The present invention is not limited to a particular typeof computer-readable storage medium, examples of which are provided forconvenience of description only.

[0065] The CVT controller 300 may also include appropriate electroniccircuitry, integrated circuits, and the like to carry out control of theCVT 10. As such, the controller 300 is used to carry out control logicimplemented in terms of software (instructions) and/or hardwarecomponents, depending upon the particular application. Additionaldescription on details of control logic implemented by the controller300 is provided later.

[0066] In order to derive information of operating conditions of the CVT10 and operator power/torque demand, the controller 300 may communicatedirectly or indirectly with at least some of various sensors and/orswitches. In FIG. 3, all such sensors and/or switches are illustrated.The various sensors include an input speed sensor 312 and an outputspeed sensor 314. The input speed sensor 312 may be provided to measurespeed of rotation of the input disc 40, while the output speed sensor314 may be provided to measure speed of rotation of the output disc 50.As the input disc 40 rotates, the input speed sensor 312 generates atrain of pulses indicative of speed of rotation of the input disc 40. Asthe output disc 50 rotates, the output speed sensor 314 generates atrain of pulses indicative of speed of rotation of the output disc 50.The various sensors include a traction roller speed sensor 316. Thetraction roller speed sensor 316 may be provided to measure speed ofrotation of the traction roller 62. As the traction roller 62 rotates,the traction roller speed sensor 316 generates a train of pulsesindicative of speed of rotation of the traction roller 62. In order togive a measured value ω_(ci) of speed of rotation of the input disc 40,the CVT controller 300 derives information of an actual speed ofrotation of the input disc 40 out of the train of pulses generated bythe input speed sensor 312. In order to give a measured value ω_(co) ofspeed of rotation of the output disc 50, the CVT controller 300 derivesinformation of an actual speed of rotation of the output disc 50 out ofthe train of pulses generated by the output speed sensor 314. In orderto give a measured value ω_(pr) of speed of rotation of the tractionroller 62, the CVT controller 300 derives information of an actual speedof rotation of the traction roller 62 out of the train of pulsesgenerated by the roller speed sensor 316.

[0067] The various sensors and/or switches also include a trunnionangular position sensor 318, a trunnion axial displacement sensor 320,an accelerator pedal sensor 322, a line pressure switch 324 and a shiftswitch 326.

[0068] The trunnion angular position sensor 318 may be provided tomeasure an actual trunnion angular position. The trunnion axialdisplacement sensor 320 may be provided to measure an actual trunnionaxial displacement from its neutral stable position. In order to give ameasured value φ of trunnion angular position, the CVT controller 300derives information of an actual trunnion angular position from theoutput of the trunnion angular position sensor 318. In order to give ameasured value y of trunnion axial displacement, the CVT controller 300derives information of an actual trunnion axial displacement from theoutput of the trunnion axial displacement sensor 320.

[0069] The CVT controller 300 derives information of an acceleratorpedal stoke or position (APS) from the output of the accelerator pedalsensor 322. The CVT controller 300 derives information of an actual linepressure PI from the output of the line pressure switch 324. The CVTcontroller 300 derives information of transmission shift position (Park,Neutral, Drive, Reverse) from the output of the shift switch 326.

[0070] The CVT controller 300 determines and applies an actuator commandto the stepper motor 188. In one exemplary embodiment (see FIG. 15), theCVT controller 300 determines motor steps rate v and generates anactuator command indicative of the determined motor steps rate v.Apparently, the motor steps rate v corresponds to CVT ratio rate. Inanother exemplary embodiment (see FIG. 16), the CVT controller 300determines motor steps u and generates an actuator command indicative ofthe determined steps u.

[0071] From the preceding description, it is to be noted that the CVT 10includes a ratio control element, in the form of the actuator shaft 190(see FIG. 2). The ratio control element is positionable in response tothe actuator command applied to the actuator 188 to establish variousspeed ratios between input and output shafts 20 and 98 of the CVT 10.

[0072] An exemplary embodiment according to the present invention can beunderstood with reference to control diagram shown in FIG. 4. In FIG. 4,the measured value ω_(ci) of speed of rotation of the input disc 40, andthe measured value ω_(co) of speed of rotation of the output disc 50 areused as system inputs. Motor steps rate v is used as a system output.

[0073] For illustration purpose, the measured value ω_(cl) of speed ofrotation of the input disc 40 is referred to as a measured value of CVTinput member or shaft, and the measured value ω_(co) of speed ofrotation of the output disc 50 as a measured value of CVT output memberor shaft speed. For the same purpose, the speed ratio between the inputdisc 40 and the output disc 50 is referred to as a CVT ratio. Thus, aspeed ratio between the measured value ω_(ci) of CVT input shaft speedand the measured value ω_(co) of CVT output shaft speed is referred toas a measured value i_(c0) of CVT ratio.

[0074] In FIG. 4, the measured value ω_(cl) of CVT input shaft speed andthe measured value ω_(co) of CVT output shaft speed are provided outsideof the CVT controller 300. To give the measured values ω_(cl) and ω_(co)of CVT input shaft speed and CVT output shaft speed, a counter countsthe number of pulses generated by the input speed sensor 312 and thenumber of pulses generated by the output speed sensor 314. The counterfeeds the counts to a timer. With the information provided by the timer,a microprocessor can compute the measured values ω_(ci) and ω_(co) ofCVT input shaft speed and CVT output shaft speed. In the case where suchmicroprocessor is provided inside the CVT controller 300 or themicroprocessor 302 (see FIG. 3) of the CVT controller 300 performs thefunction, the measured value ω_(cl) of CVT input shaft speed and themeasured value ω_(co) of CVT output shaft speed are provided inside theCVT controller 300. In any case, the measured values ω_(cl) and ω_(co)cannot avoid influences of noise that may occur in the train of pulsesgenerated by the input and output speed sensors 312 and 314.

[0075] With continuing reference to FIG. 4, a measured CVT ratiogenerator 340 is provided. The measured value ω_(cl) of CVT input shaftspeed and the measured value ω_(co) of CVT output shaft speed are usedas inputs to the measured CVT ratio generator 340. The measured CVTratio generator 340 obtains information on an actual CVT ratioestablished in the CVT 10 to give a measured value i_(c0) of CVT ratio.The measured CVT ratio generator 340 outputs the measured value i_(c0)of CVT ratio. In this embodiment, the measured value i_(c0) of CVT ratiois given by dividing the measured value ω_(ci) of CVT input shaft speedby the measured value ω_(co) of CVT output shaft speed. Thus, themeasured value i_(c0) is expressed as: $\begin{matrix}{i_{c0} = \frac{\omega_{c\quad i}}{\omega_{c\quad o}}} & (1)\end{matrix}$

[0076] The present invention is not limited to this example of giving ameasured value i_(c0) of CVT ratio. There are various examples of givinga measured value i_(c0) of CVT ratio.

[0077] Estimating a measured value i_(c0) of CVT ratio from a measuredvalue φ_(o) of trunnion angular position φ is one example. In this case,the estimation is made using the following equation. $\begin{matrix}{i_{c} = {\frac{1 + \eta - {2{\cos \left( {{2\theta} - \varphi} \right)}}}{1 + \eta - {\cos \quad \varphi}}i_{e}}} & (2)\end{matrix}$

[0078] where: i_(c) is an estimated value of CVT ratio;

[0079] η, θ and i_(e) are constants that are determined according tomechanical specification of the CVT 10.

[0080] Estimating values ω_(ci) and ω_(co) of CVT input shaft speed andCVT output shaft speed from a measured value ω_(pr) of traction rollerspeed and a measured value φ_(o) of trunnion angular position φ isanother example. In this case, a measured value i_(c0) of CVT ratio iscalculated after making the estimation of ω_(ci) and ω_(co) is madeusing the following equations. $\begin{matrix}{\omega_{c\quad i} = {\frac{\sin \quad \theta}{1 + \eta - {\cos \quad \varphi}}\omega_{p\quad r}}} & (3) \\{\omega_{c\quad o} = {\frac{\sin \quad \theta}{1 + \eta - {\cos \left( {{2\theta} - \varphi} \right)}}\omega_{p\quad r}}} & (4)\end{matrix}$

[0081] A desired CVT ratio generator 342 is provided. An APS from theaccelerator pedal sensor 322 and measured value ω_(co) of CVT outputshaft speed are used as inputs to the desired CVT ratio generator 342.First, the measured value ω_(co) of CVT output shaft speed is processedto give a vehicle speed VSP. The vehicle speed VSP is expressed as:

VSP=k _(v)ω_(co)  (5)

[0082] where: k_(v) is a constant that is determined accounting for theoverall gear ratio from the output shaft 98 (see FIG. 1) to a tire avehicle installed with the CVT 10 and the radius of the tire.

[0083] In the embodiment, the desired CVT ratio generator 342 includes alook-up map in computer-readable storage media 304 (see FIG. 3). Oneexample of such a look-up map is a shift map shown in FIG. 13. In FIG.13, contour lines are illustrated for different values of APS, such as0/8, 1/8, . . . 8/8. Each line represents varying of desired valueω_(te) of engine speed with different values of vehicle speed VSP forthe same value of accelerator pedal position APS.

[0084] The desired CVT ratio generator 342 calculates a desired ratioi_(ct) between the desired value ω_(te) of engine speed and the measuredvalue ω_(co) of CVT output shaft speed. This ratio is expressed as$\begin{matrix}{i_{c\quad t} = \frac{\omega_{t\quad c}}{\omega_{c\quad o}}} & (6)\end{matrix}$

[0085] The desired CVT ratio generator 342 includes a filter that isexpressed as

(i _(c)*)′=−c _(r) i _(c) *+c _(r) i _(ct)  (7)

[0086] where: c_(r) is a constant equivalent to a time constant that isdetermined accounting for shift feel.

[0087] The filter expressed by the equation (7) processes the desiredratio i_(ct) to give a desired value i_(c)* of CVT ratio. The desiredCVT ratio generator 342 outputs the desired value i_(c)* of CVT ratio.

[0088] There is precision requirement that, in the CVT 10, at least oneor some CVT ratios should be established with excellent precision. Toexpress such precision requirement, a precision required CVT ratiogenerator 344 is provided. The precision required CVT ratio generator344 outputs a precision required value of CVT ratio. There are variousexamples of the precision required value of CVT ratio. One example isthe largest value i_(cl) of CVT ratio, which is used upon moving thevehicle from standstill and defines the lower limit of a range of CVTratios that the CVT 10 is capable of establishing. Another example isthe smallest value i_(ch) of CVT, which defines the higher limit of therange of CVT ratios. Other example is a value of CVT ratio to beestablished to provide a GNP in an IVT.

[0089] In one exemplary embodiment, the precision required CVT ratiogenerator 344 outputs both largest and smallest values i_(cl) and i_(ch)of CVT ratio, which defines the lower and upper limits of a range of CVTratios that the CVT 10 is capable of establishing. So establishing thelargest and smallest values i_(cl) and i_(ch) of CVT ratio to meet theprecision requirement narrows margins needed at mechanical limits (seeFIG. 27) sufficiently, allowing a range of CVT ratios to extend towardthe mechanical limits. This makes it possible to set a sufficiently widerange of CVT ratios without modifying the size of a CVT unit to increasea range of CVT ratios between mechanical limits. So setting thesufficiently wide range of CVT ratios allows use of appropriate CVTratios for good fuel consumption by a prime mover, for example, anengine, during operation at high vehicle speeds, enhancing fuel economy.As the largest value i_(cl) of CVT ratio is established with excellentprecision every time the vehicle is to move from standstill, providingthe vehicle operator with the same acceleration feel.

[0090] With continuing reference to FIG. 4, a noise estimator 346 isprovided. The noise estimator 346 estimates the frequency of noise andthe magnitude thereof. The input speed sensor 312 is provided togenerate a train of synchronous pulses with rotation of input disc 40.The output speed sensor 314 is provided to generate a train ofsynchronous pulses with rotation of output disc 50. The train ofsynchronous pulses from the input speed sensor 312 is processed, forexample, by calculating period of the pulses or frequency thereof. Basedon the calculated period or frequency, the measured value ω_(ci) of CVTinput shaft speed is given. Likewise, the train of synchronous pulsesfrom the output speed sensor 314 is processed, for example, bycalculating period of the pulses or frequency thereof. Based on thecalculated period or frequency, the measured value ω_(co) of CVT outputshaft speed is given. Using the equation (1), the measured value i_(c0)of CVT ratio is given by calculation based on the measured values ω_(ci)and ω_(co). In this case, the noise estimator 346 estimates the measuredvalue i_(c0) of CVT ratio using the equation as follows:

i _(c0) =i _(cp)(1+α₁ sin ω₁ t+α₂ sin ω₂ t)  (8)

[0091] where: i_(cp) is a pure value of CVT ratio that is free fromnoise;

[0092] α₁ is constant that is determined accounting for angulardisplacement and the processing precision of teeth of a wheel of theinput speed sensor 312;

[0093] α₂ is constant that is determined accounting for angulardisplacement and the processing precision of teeth of a wheel of theoutput speed sensor 314;

[0094] ω₁ is a measured value of frequency of synchronous pulses of theinput speed sensor 312 with rotation of input disc 40; and

[0095] ω₂ is a measured value of frequency of synchronous pulses of theoutput speed sensor 314 with rotation of output disc 50.

[0096] In the equation (8), the pure value i_(cp) of CVT ratio appears.This value i_(cp) may be derivable from the measured value i_(cO) of CVTratio or an estimated value i_(c) of CVT ratio, which will be describedlater.

[0097] If period T_(in) of the synchronous pulses of the input speedsensor 312 is measured, the measured frequency ω₁ is given bycalculating the equation as: $\begin{matrix}{~{\omega_{1} = \frac{2\pi}{T_{in}}}} & \text{(9-1)}\end{matrix}$

[0098] If period T_(out) of the synchronous pulses of the output speedsensor 314 is measured, the measured frequency ω₂ is given bycalculating the equation as: $\begin{matrix}{\omega_{2} = \frac{2\pi}{T_{out}}} & \text{(9-2)}\end{matrix}$

[0099] Noise i_(cd) of the measured value i_(c0) of CVT ratio can bederived from the equation (8) and expressed as:

i _(cd) =i _(cp)(α₁ sin ω₁ t+α ₂ sin ω₂ t)  (10)

[0100]FIG. 11 illustrates the noise i_(cd) in magnitude at frequenciesω₁ and ω₂. The noise estimator 346 makes estimates (ω₁, i_(cp)α₁) and(ω₂, i_(cp)α₂) as frequencies of noise and magnitudes thereof at thefrequencies. The frequency of noise ω₁ is proportional to the measuredvalue ω_(ci) of CVT input shaft speed. The lower the measured valueω_(ci) of CVT input shaft speed, the lower the frequency of noise ω₁. Inthe case a band reject filter is used, the band of frequency to berejected is lowered as the CVT input shaft speed drops. This measure iseffective in suppressing the standing deviation in CVT ratio to keep itwithin a dead zone even if the frequency of noise ω₁ changes due tochange in CVT input shaft speed. The frequency of noise ω₂ isproportional to the measured value ω_(co) of CVT output shaft speed.

[0101] With continuing reference to FIG. 4, a filter 348 is provided.The measured value i_(c0) of CVT ratio is used as input of the filter348. The filter 348 processes the measured value i_(c0) of CVT ratio ina manner to refine the information of the actual CVT ratio to give anestimated value i_(c) of CVT ratio. The filter 348 outputs the estimatedvalue i_(c) of CVT ratio. There are various examples of the filter 348.One example is a filter 348A illustrated in FIG. 5, which employs a lowpass filter W₁. Another example is a filter 348B illustrated in FIG. 7,which employs an observer as a low pass filter. Other example is afilter 348C illustrated in FIG. 10, which employs a band reject filter.

[0102] With reference also to FIGS. 5 and 6, the low pass filter W₁ isexpressed as: $\begin{matrix}{W_{1} = \frac{\omega_{f}^{n}}{\left( {s + \omega_{f}} \right)^{n}}} & (11)\end{matrix}$

[0103] where: s is the Laplacian;

[0104] ω_(f) is cutoff frequency;

[0105] n is exponent determined accounting for the magnitude of noiseand CVT ratio rate.

[0106]FIG. 6 is a gain vs., frequency characteristic of the low passfilter W₁. As it clearly shows, the gain within a higher frequency bandthan the cutoff frequency ω_(f) becomes small as the exponent n becomeslarge. Accounting for the magnitude of noise and CVT ratio rate, anappropriate value should be set as the exponent n.

[0107] With reference now to FIGS. 7 and 8, the measured value i_(c0) isconverted into a measured value of trunnion angular position φ using thelook-up table shown in FIG. 9. The measured value of trunnion angularposition φ is used as input to an observer of the filter 348B. Thisobserver provides an estimated value {circumflex over (φ)} of trunnionangular position. This estimated value {circumflex over (φ)} isconverted into an estimated value i_(c) of CVT ratio using the look-uptable shown in FIG. 9. The filter 348B outputs the estimated value i_(c)of CVT ratio.

[0108] Prior to further description on the observer of the filter 348B,a mathematical model of the CVT 10 is explained. In this model, a motorsteps rate v, i.e., the first time derivative of motor steps u, is usedas the input, and a trunnion angular displacement φ, a trunnion axialdisplacement y, and motor steps u are used as state indicativequantities. The mathematical model may be expressed as:

(x)′=Ax+Bu  (12)

[0109] where, ${x = \begin{bmatrix}\varphi \\y \\u\end{bmatrix}},{A = \begin{bmatrix}0 & f & 0 \\{{- a_{1}}g} & {{- a_{2}}g} & {b\quad g} \\0 & 0 & 0\end{bmatrix}},{B = \begin{bmatrix}0 \\0 \\1\end{bmatrix}}$

[0110] g is a variable dependent on line pressure Pl, which variable isobtained from a look-up table, not shown, versus line pressure Pl;

[0111] a₁, a₂ and b are constants that are determined according to themechanical specification of the CVT 10;

[0112] f is a time dependent variable determined depending upon thetrunnion angular displacement φ and a speed of rotation of a CVT inputshaft or a CVT output shaft or a CVT traction roller.

[0113] For example, using the measured value ω_(co) of CVT output shaftspeed, the time dependent variable f may be expressed as:$\begin{matrix}{f = \left\{ {1 + \eta - {{\cos \left( {{2\theta} - \varphi} \right)}\frac{\cos \left( {\theta - \varphi} \right)}{\left( {1 + \eta} \right)R_{0}\sin \quad \theta}}} \right.} & (13)\end{matrix}$

[0114] where: η, θ and R₀ are constants that are determined according tothe mechanical specification of the CVT 10.

[0115] In order to provide an estimated value of state quantity x of theCVT 10, the observer is used, which may be expressed as:

=A{circumflex over (x)}+Bu+H(φ−{circumflex over (φ)})  (14)

[0116] where: {circumflex over (x)}=[{circumflex over (φyu)}]^(T);

[0117] {circumflex over (φ)} is an estimated value of trunnion angularposition;

[0118] ŷ is an estimated value of trunnion axial displacement;

[0119] û is an estimated value of the number of motor steps;

[0120] H=[h₁ h₂ h₃]^(T), which is an observer gain that specifies thespeed of estimation by the observer.

[0121] The matrix components of the observer gain H are defined as:

h ₁=2ζ_(o)ω_(f)+ω_(f) −a ₂ g  (15) $\begin{matrix}{h_{2} = \frac{\omega_{f}^{2} + {2\zeta_{o}\omega_{f}^{2}} - {a_{2}{g\left( {{2\zeta_{o}\omega_{f}} + \omega_{f} - {a_{2}g}} \right)}} - {a_{1}g\quad f}}{f}} & (16) \\{h_{3} = \frac{\omega_{f}^{3}}{bgf}} & (17)\end{matrix}$

[0122] As mentioned before, the input to this observer is trunnionangular position φ that is found in the look-up table shown in FIG. 9using the measured value i_(co) of CVT ratio.

[0123] Subtracting both sides of the equation (14) from both sides ofthe equation (12) can give the dynamic characteristic of deviation eexpressed as:

{dot over (e)}=(A−HC)e  (18)

[0124] where: e=x−{circumflex over (x)};

[0125] C is expressed as

C=[1 0 0]  (19)

[0126] From the equation (18), we obtain its characteristic equationthat is expressed as:

(S ²+2ζ_(o)ω_(f) S+ω_(f) ²)(S+ω _(f))=0  (20)

[0127] As shown in FIG. 8, the observer has a low band passcharacteristic from trunnion angular displacement φ to the estimatedvalue {circumflex over (φ)} of trunnion angular displacement. Thisobserver should be used as a low pass filter of the filter 348B. Asmentioned before, an estimated value i_(c) of CVT ratio is obtained fromthe look-up table shown in FIG. 9 using the estimated value {circumflexover (φ)} of trunnion angular displacement.

[0128] The filter 348A uses the low pass filter W₁ and the filter 348Buses the observer that behaves as a low pass filter. Cutoff frequencyω_(f) of such low pass filters is determined at a filter and commandgenerator manager that will be described later.

[0129] With reference now to FIGS. 10-12, the filter 348C uses a bandreject filter or notch filter instead of the low pass filters. In thiscase, the band reject filter has reject bands to reject signal at thefrequencies ω₁ and ω₂ of noise estimated at the noise estimator 346.FIG. 11 illustrates the noise estimated by the noise estimator 346. FIG.12 illustrates a gain vs., frequency of the band reject filter that hasreject bands at the frequencies ω₁ and ω₂ of noise estimated. Using suchband reject filter or notch filter, the filter 348C processes themeasured value i_(co) of CVT ratio to give an estimated value i_(c) ofCVT ratio. As mentioned before, the frequency ω₁ of noise isproportional to the measured value ω_(ci) of CVT input shaft speed. Thelower the measured value ω_(cl) of CVT input shaft speed, the lower thefrequency ω₁. The reject band of frequencies is lowered as the CVT inputshaft speed drops to eliminate the noise at the frequency ω₁. Thefrequency ω₂ of noise is proportional to the measured value ω_(co) ofCVT output shaft speed. The reject band of frequencies is lowered as theCVT output shaft speed drops to eliminate the noise at the frequency ω₂.

[0130] Turning back to FIG. 7, the measured value i_(c0) of CVT ratio isused as the single input to the observer used in the filter 348B, andthe observer can provide an estimated value i_(c) of CVT ratio. In anexemplary embodiment, in addition to the measured value i_(c0) of CVTratio, an actuator command, such as a motor steps rate v or motor stepsu, is used as another input to the observer used in the filter 348B.Using the actuator command as the input, the observer can estimate notonly the CVT ratio but also trunnion axial displacement. In this case,the provision of a trunnion axial displacement sensor is no longerneeded, leading to reduction in manufacturing cost. Besides, thetrunnion axial displacement can be estimated with excellent accuracy,making it possible to maintain a precision required value of CVT ratio.

[0131] With continuing reference to FIG. 4, a command generator 350 isprovided. The estimated value i_(c) of CVT ratio and the desired valuei_(c)* of CVT ratio are used as inputs to the command generator 350. Thecommand generator 350 determines an actuator command such that theactuator command remains unaltered when a deviation of the estimatedvalue i_(c) of CVT ratio from the desired value i_(c)* of CVT ratiostays within a dead zone. In one exemplary embodiment to be explainedlater in connection with FIG. 15, the command generator 350 determines amotor steps rate v as the actuator command. The command generator 350applies the motor steps rate v to the actuator, in the form of steppermotor 188, of the CVT 10. In another exemplary embodiment to beexplained later in connection with FIG. 16, a command generator 350Adetermines motor steps u as the actuator command. The command generator350A applies the motor steps u to the stepper motor 188 of the CVT 10.

[0132] With reference now to FIG. 15, the command generator 350 isdesigned to maintain a predetermined response characteristic of theestimated value i_(c) of CVT ratio to a change in the desired valuei_(c)* of CVT ratio. The estimated value i_(c) is used as input to a box360. The estimated value i_(c) is converted to an estimated value oftrunnion angular position φ using the look-up table in FIG. 9. Inaddition to the estimated value i_(c) of CVT ratio, the estimated valueof trunnion angular position φ, trunnion axial displacement y, and motorsteps u are used as other inputs to a box 360. At box 360, the first andsecond derivatives of CVT ratio {dot over (i)}c and ïc are given by thefollowing partial differential equations. $\begin{matrix}{{\overset{.}{i}}_{c} = {\frac{\partial i_{c}}{\partial\varphi}{fy}}} & (21) \\{{\overset{¨}{i}}_{c}\quad = {{\frac{\partial^{2}i_{c}}{\partial\varphi^{2}}f^{2}y^{2}} + {\frac{\partial i_{c}}{\partial\varphi}\overset{.}{f}y} + {\frac{\partial i_{c}}{\partial\varphi}{{fg}\left( {{{- a_{1}}\quad \varphi} - {a_{2}y} + {bu}} \right)}}}} & (22)\end{matrix}$

[0133] where:$\frac{\partial i_{c}}{\partial\varphi}\quad {and}\quad \frac{\partial^{2}i_{c}}{\partial\varphi^{2}}$

[0134] are found in maps, not shown, using the estimated value oftrunnion angular position φ;

[0135] {dot over (f)} is expressed by the following partial differentialequation; $\begin{matrix}{\overset{.}{f} = {{\frac{\partial f}{\partial\varphi}{fy}} + {\frac{\partial f}{\partial\omega_{co}}\omega_{co}}}} & (23)\end{matrix}$

$\frac{\partial f}{\partial\varphi}\quad {and}\quad \frac{\partial f}{\partial\omega_{co}}$

[0136] are found in maps, not shown, using the estimated value oftrunnion angular position φ.

[0137] In the equation (23), the second term$\frac{\partial f}{\partial\omega_{co}}\omega_{co}$

[0138] on the right side may be negligibly small and thus regarded as 0(zero) because a change in the measured value ω_(co) is very slow.

[0139] The desired value i_(c)* of CVT ratio, estimated value i_(c) ofCVT ratio, and the first and second derivative of CVT ratio {dot over(i)}c and ïc are used as inputs to a box 362. At box 362, a controlerror σ₀ is determined. The control error σ₀ is an error between theactual response of the actual CVT ratio to a change in the desired CVTratio and a desired response. The control error σ₀ is expressed as:

σ₀ =ï _(c)+2ζ_(n) ω _(n{dot over (i)}) _(c) +ωn ²(ic−ic*)  (24)

[0140] where: ζ_(n) is the damping coefficient of desired response;

[0141] ω_(n) is the natural frequency.

[0142] The control error σ₀ and a dead zone expressed in terms of adeviation e_(d) are used as inputs to a box 364. At box 364, the controlerror σ₀ is processed to give a processed control error σ by performingcontrol logic as follows:

[0143] If σ₀≧e_(d), then σ=σ₀−e_(d)

[0144] If |σ₀|<e_(d), then σ=0

[0145] If σ₀≦−e_(d), then σ=σ₀+e_(d)

[0146] The processed control error is used as input to a box 366. At box366, a motor steps rate v is determined as the actuator command. Themotor steps rate v is expressed as: $\begin{matrix}{v = {{- K}\frac{\sigma}{\left| \sigma \middle| {+ ɛ} \right.}}} & (25)\end{matrix}$

[0147] where: ε is a positive constant that provides continuity ofrelationship of v with respect to σ when σ is in the neighborhood of 0(zero);

[0148] K is the maximum speed at which the stepper motor 188 canoperate.

[0149] With reference next to FIG. 16, another example of commandgenerator designated at 350A is explained. As different from the commandgenerator 350 shown in FIG. 15, the command generator 350A determinesmotor steps u. The estimated value i_(c) of CVT ratio and the desiredvalue i_(c)* of CVT ratio are used as inputs to a box 370. At box 370, adeviation e₀ between i_(c) and i_(c)* (e₀=i_(c)−i_(c)*) is determined.

[0150] The deviation e₀ and a dead zone expressed in terms of adeviation e_(d) are used as inputs to a box 372. At box 372, thedeviation e₀ is processed to give a processed deviation e by performingcontrol logic as follows:

[0151] If e₀≧e_(d), then e=e₀−e_(d)

[0152] If |e₀|<e_(d), then e=0

[0153] If e₀−e_(d), then e=e₀+e_(d)

[0154] The processed deviation e is used as input to a box 374. At box374, motor steps u is determined as the actuator command. The motorsteps u is expressed as: $\begin{matrix}{u = {{K_{P}e} + {\frac{K_{I}}{s}e}}} & (26)\end{matrix}$

[0155] where: K_(p) is the proportional gain;

[0156] K_(I) is the integral gain;

[0157] s is the Laplacian.

[0158] With reference back to FIG. 4, a filter and command generatormanager 352 is provided. The filter and command generator manager 352narrows the dead zone e_(d) to meet precision requirement upondetermination that the desired value i_(c)* of CVT ratio has beenaccomplished. Besides, the filter and command generator manager 352adjusts the filter 348 to gain requirement for keeping the magnitude ofsignal at frequency of noise within the narrowed dead zone.

[0159] In the exemplary embodiment, the precision required CVT ratiogenerator 344 outputs the largest and smallest values i_(cl) and i_(ch)of CVT ratio as examples of a precision required value of CVT ratio. Theprecision required value, i_(cl) or i_(ch), for example, and the desiredvalue i_(c)* are used as inputs to the filter and command generatormanager 352 for determination whether or not there is precisionrequirement that the precision required value, i_(cl) or i_(ch), forexample, be held with excellent precision. In the embodiment, the filterand command generator manager 352 determines that the precisionrequirement exists when the desired value i_(c)* of CVT ratio and theprecision required value i_(cl) or i_(ch) match with each other.

[0160] When a need remains to meet the precision requirement, the filterand command generator manager 352 determines whether or not the desiredvalue i_(c)* has been accomplished. In the embodiment, for example, itis determined that the desired value i_(c)* has been accomplished whenthe estimated value i_(c) of CVT ratio and the desired value i_(c)*match with each other.

[0161] As mentioned before, the filter and command generator manager 352narrows the dead zone e_(d) to meet the precision requirement upondetermination that the desired value i_(c)* of CVT ratio has beenaccomplished. This situation continues until the precision requirementdisappears. Immediately after the precision requirement has disappearedor when the precision requirement does not exist, the filter and commandgenerator manager 352 reinstates the dead zone e_(d), so that the deadzone e_(d) is wide enough to permit ratio change without hunting. In theembodiment, the dead zone e_(d) is given by summing the magnitudes ofnoise i_(cp)α₁ and i_(cp)α₂ when there is no precision requirement.

[0162] In coordination with the dead zone e_(d) wide enough to permitratio change without hunting, the filter and command generator manager352 adjusts the filter 348 to gain requirement for keeping good responsecharacteristic by minimizing a delay of a change in the estimated valuei_(c) of CVT ratio to a change in the measured value i_(c0) of CVTratio. In the case, the low pass filter, which exhibits the gain vs.,frequency characteristic shown in FIG. 6, is used or the observer, whichexhibits the gain vs., frequency characteristic shown in FIG. 8 is used,the filter and command generator manager 352 selects a sufficiently highfrequency as the cutoff frequency ω_(f) to meet the gain requirement.

[0163] In the embodiment, when the estimated value i_(c) of CVT ratioand the desired value i_(c)* of CVT ratio match with each other afterthe desired value i_(c)* of CVT ratio and the precision required valuei_(cl) or i_(ch) of CVT ratio have matched with each other, the filterand command generator manager 352 sets the narrowed dead zone e_(d). Thefilter and command generator manager 352 finds a value of CVT ratiointerval Δi_(c) versus the measured value i_(c0) of CVT ratio or theestimated value i_(c) of CVT ratio from a look-up table shown in FIG.14. The filter and command generator 352 uses the value of CVT ratiointerval Δi_(c) in determining the narrowed dead zone e_(d). The look-uptable shown in FIG. 14 provides a CVT ratio interval Δi_(c) that isdetermined by the resolution of the stepper motor 188 at a CVT ratio.

[0164] In coordination with the narrowed dead zone e_(d), the filter andcommand generator manager 352 adjusts the filter 348 to gain requirementfor keeping the magnitude of signal at frequency of noise within thenarrowed dead zone e_(d). In the case, the low pass filter, whichexhibits the gain vs., frequency characteristic shown in FIG. 6, is usedor the observer, which exhibits the gain vs., frequency characteristicshown in FIG. 8 is used, the filter and command generator manager 352selects a sufficiently low frequency as the cutoff frequency ω_(f) tomeet the gain requirement. With the cutoff frequency ω_(f) set at suchlow frequency, the low pass filter 348 or 348A or 348B provides, atfrequencies of noise ω₁ and ω₂, gains G₁ and G₂ low enough, as shown inFIG. 6 or 8, to suppress level of noise contained in the estimated valuei_(c) of CVT ratio to a sufficiently low level.

[0165] As is readily understood from FIG. 6 or 8, the cutoff frequencyω_(f) of a low pass filter determines gains G₁ and G₂ at frequencies ofnoise ω₁ and ω₂. As shown in FIG. 11, the magnitudes of noise atfrequencies ω₁ and ω₂ are i_(cp)α₁ and i_(cp)α₂, respectively, accordingto the calculation at the noise estimator 346. Keeping the signal at thefrequencies ω₁ and ω₂ within the narrowed dead zone e_(d) must hold thefollowing relationship.

e _(d) >i _(cp)(α₁ G ₁+α₂ G ₂)  (27)

[0166] The frequency of cutoff frequency ω_(f) should be set to hold therelationship as expressed by the formula (27).

[0167] The formula (27) clearly tells that narrowing the dead zone e_(d)demands reductions in the magnitudes of gains G₁ and G₂ to keep thesignal at frequencies of noise ω₁ and ω₂ within the narrowed dead zonee_(d). This causes the standing deviation, if any, to shrinksufficiently.

[0168] The formula (27) also tells that increasing of pure value i_(cp)of CVT ratio demands reduction in the magnitudes of gains G₁ and G₂ atthe frequencies of noise ω₁ and ω₂. The pure value i_(cp) of CVT ratioincreases as the actual CVT ratio within the CVT 10 shifts down. What isneeded to cope with this situation is to lower the cutoff frequencyω_(f) so as to reduce the magnitudes of gains G₁ and G₂ at thefrequencies of noise ω₁ and ω₂.

[0169] In the above description, the cutoff frequency ω_(f) of a lowpass filter only has been relied upon to reduce the magnitude of gainsG₁ and G₂ at the frequencies of noise ω₁ and ω₂. In the case the lowpass filter W₁ that is expressed as the equation (11) is used,increasing the exponent n causes reductions in the magnitudes of gainsG₁ and G₂ at the frequencies of noise ω₁ and ω₂ as readily seen fromFIG. 6.

[0170] Accounting for the case where the actual noise contained in themeasured value i_(c0) of CVT ratio exceeds the estimates i_(cp)α₁ andi_(cp)α₂ has caused the filter and command generator manager 352 toreduce a control gain at the command generator 350 upon determinationthat the desired value i_(c)* of CVT ratio has been accomplished afterthe desired value i_(c)* of CVT ratio and the precision required valuei_(cl) (or i_(ch)) have matched with each other. Reducing the controlgain causes a delay in response rate of a change in the estimated valuei_(c) of CVT ratio to a change in the desired value i_(c)* of CVT ratio,effectively suppressing vibration of CVT ratio due to noise. Withreference to FIG. 15, the term ω_(n) (see box 362) or ε (see box 366) orK (see box 366) may be varied to reduce the control gain at the commandgenerator 350.

[0171] The flow chart in FIG. 17 illustrates a control routine 380 ofthe preferred implementation of the present invention. Themicroprocessor 302 of CVT controller 300 (see FIG. 3) repeats executionof the control routine 380 at regular interval of, for example, 10milliseconds. At input box 382, the controller inputs information ofmeasured value ω_(co) of CVT output shaft, measured value ω_(cl) of CVTinput shaft, trunnion axial displacement y, accelerator pedal position(or depression) APS and line pressure Pl.

[0172] At box 384, the controller calculates vehicle speed VSP(=k_(v)ω_(co)). At box 386, the controller determines a measured valuei_(c0) of CVT ratio by dividing ω_(ci) by c_(co). At box 388, thecontroller determines a desired value i_(c)* of CVT ratio by executing adesired CVT ratio generating sub-routine to be described later inconnection with FIG. 18. At box 390, the controller estimatesfrequencies of noise and the amplitudes at the frequencies (ω₁,i_(cp)α₁) and (ω₂, i_(cp)α₂).

[0173] At interrogation box 392, the controller determines whether ornot the estimated value i_(c) of CVT ratio and the desired value i_(c)*of CVT ratio match with each other after the desired value i_(c)* of CVTratio and the precision required value i_(cl) or i_(ch) of CVT ratiohave matched with each other. If this is the case, the control logicgoes to box 394. If this is not the case, the control logic goes to box396.

[0174] At box 394, the controller determines the CVT ratio intervalΔi_(c) from the look-up table shown in FIG. 14. The controllerdetermines width of dead zone d (=2×e_(d)) as a function of the CVTratio interval Δi_(c). The controller determines a cutoff frequencyω_(fs) and sets the determined frequency ω_(fs) as a cutoff frequencyω_(f) of an observer that exhibits a low pass filter characteristic asshown in FIG. 8.

[0175] At box 396, the controller determines dead zone e_(d) as afunction of sum (i_(cp)α₁+i_(cp)α₂). The controller determines a cutofffrequency ω_(ft) (ω_(ft)>ω_(fs)) and sets the determined frequencyω_(fs) as a cutoff frequency ω_(f) of an observer that exhibits a lowpass filter characteristic as shown in FIG. 8.

[0176] After setting dead zone and cutoff frequency at box 394 or 396,the control logic goes to box 398. At box 398, the controller computesthe observer that has been explained before in connection with FIGS. 7and 8 to process or filter the measured value i_(c0) of CVT ratiothereby to determine an estimated value i_(c) of CVT ratio.

[0177] At box 400, the controller determines motor steps rate v byexecuting a command determining sub-routine to be described later inconnection with FIG. 19.

[0178] At output box 402, the controller outputs the determined motorsteps rate v as stepper motor command.

[0179] The flow chart in FIG. 18 illustrates the desired CVT ratiogenerating sub-routine now generally designated at 410. At box 412, thecontroller determined a desired or attainable value ω_(te) of enginespeed from the look-up map shown in FIG. 13. At box 414, the controllerdetermines a desired value i_(ct) of speed ratio by dividing ω_(te) byω_(co). At box 416, the controller determines the desired value i_(c)*by calculates the filter expressed as(i_(c)*)′=−c_(r)i_(c)*+c_(r)i_(ct).

[0180] The flow chart in FIG. 19 illustrates the command determiningsub-routine now generally designated at 420. At box 422, the controllerdetermines an estimated value of trunnion angle φ from the look-up tableshown in FIG. 9. At box 424, the controller determines the first andsecond derivatives of the estimated value i_(c) of CVT ratio bycalculating the partial differential equations (21) and (22). At box426, the controller determines a control error σ₀ by calculating theequation (24). At box 428, the controller determines a processed or afinal control error σ by conducting control logic as follows:

[0181] If σ₀≧e_(d), then σ=σ₀−e_(d)

[0182] If |σ₀<e_(d), then σ=0

[0183] If σ₀≦−e_(d), then σ=σ₀+e_(d)

[0184] At box 430, the controller determines motor steps rate v bycalculating the equation (25).

[0185]FIG. 20 is a simulation result of confirming the effectiveness ofthe embodiment according to the present invention. The desired valuei_(c)* of CVT ratio was changed from a value of 1.7 to another value of1.9, which is a precision required value i_(cl) of CVT ratio, and thenback to the value of 1.7. The width of ordinary wide dead zone was 0.02,and the width of narrowed dead zone was 0.002. The result clearly showsthat standing deviation is considerably large at the value of 1.7. Italso clearly shows that, at the value of 1.9, standing deviation issmall and negligible, so that the precision required value of CVT ratiois held with excellent precision.

[0186] With reference now to FIGS. 21 and 22, it is described that thepresent invention may be implemented in a CVT that is configured to forman infinitely variable transmission (IVT).

[0187]FIG. 21 is a schematic diagram of the IVT, which is substantiallythe same as the structure shown in FIG. 1 of and described in thecommonly assigned U.S. Pat. No. 6,351,700 B1, Muramoto et al., issuedFeb. 26, 2002 or the commonly assigned U.S. Pat. No. 6,317,672 B1,Kuramoto et al., issued Nov. 13, 2001. Both of these two commonlyassigned United States Patents have been incorporated herein byreference in their entirety.

[0188] In FIG. 21, the IVT is generally designated at 440. The IVT 440comprises an IVT input shaft 442 to be driven by an engine, not shown,of a vehicle, and an IVT output shaft 446. A CVT includes a dual cavitytoroidal drive 448. The dual cavity toroidal drive 448 is substantiallythe same as the dual cavity toroidal drive 12 except the provision of achain sprocket 444 instead of the output gear 54. The chain sprocket 444is fixedly connected to inboard output discs 50 and 52. Like referencenumerals are used to designate like or similar parts in FIGS. 1 and 21.The input shaft 442 drives outboard input discs 40 and 42 of the dualcavity toroidal drive 448.

[0189] A planetary gearing 450 is connected to the output shaft 446. Adirect clutch 452 and a power recirculation clutch 454 are provided. Theplanetary gearing 450 is a simple planetary gear set and includes a sungear 456, a ring gear 458, and a pinion carrier 460. The pinion carrier460 supports a plurality of pinions, each being in mesh engagementbetween the sun and ring gears 456 and 458.

[0190] An input gear 466 is fixedly coupled to the input shaft 442 forrotation therewith. The input gear 466 is in mesh with an output gear464. The output gear 464 is mounted for relative rotation about theoutput shaft 446, and fixedly connected to a clutch drum 455 of thepower recirculation clutch 454.

[0191] The ring gear 458 is fixedly connected to the output shaft 446for rotation therewith. The sun gear 456 is fixedly connected to a chainsprocket 463 via a hollow sleeve 457 that is supported for relativerotation about the input shaft 446. The chain sprocket 463 is fixedlyconnected to a clutch drum 453 of the direct clutch 452. A chain 462drivingly interconnects the chain sprockets 444 and 463.

[0192] The output shaft 446 has an output gear 468. The output gear 468is in mesh with a final gear 470 of a deferential with a pair of axles472 and 474.

[0193] The direct clutch 452 has a first hydraulic servo 480 and a firstsolenoid valve 482. The first solenoid valve 482 regulates hydraulicpressure applied to the first hydraulic servo 480. The hydraulicpressure determines a clutch engagement force, with which the directclutch 452 is engaged. The power recirculation clutch 454 has a secondhydraulic servo 490 and a second solenoid valve 492. The second solenoidvalve 492 regulates hydraulic pressure applied to the second hydraulicservo 490. This hydraulic pressure determines a clutch engagement force,with which the power recirculation clutch 454 is engaged.

[0194] With reference to FIG. 22, the vertical axis represents thereciprocal of IVT ratio, and the horizontal axis represents CVT ratio.For operation in power recirculation mode, the clutches 454 and 452 areengaged and disengaged, respectively. For operation in direct mode, theclutches 454 and 452 are disengaged and engaged, respectively.

[0195] As is well known in the art of toroidal drive tractiontransmissions, pivoting of axles of traction rollers alters the CVTratio. When the traction roller axles are in the positions, namely, lowposition, illustrated in FIG. 21, their associated traction rollers 56,58, 60 and 62 make contact with their input discs 40, 42 at minimumradius and with their output disc 50, 52 at maximum radius: the CVTratio is therefore the largest. At the other extreme, when the tractionroller axles are in the positions, namely, high positions, notillustrated, the traction rollers 56, 58, 60 and 62 make contact withtheir input discs 40, 42 at maximum radius and with their output discs50, 52 at minimum radius: the CVT ratio is therefore the smallest.

[0196] Assume that, with the clutches 454 and 452 are engaged anddisengaged, respectively, the traction roller axles are in the highpositions in which their associated traction rollers 56, 58, 60 and 62make contact with their input discs 40 and 42 at maximum radius and withtheir output discs 50 and 52 at minimum radius. For a given speed ofrotation of the IVT input shaft 442, the IVT output shaft 446 will berotating at maximum speed in reverse direction. If now the inclinationof the traction roller axles is progressively changed so that they movetowards the opposite extreme of their angles of movement, the resultantof unchanging speed of pinion carrier 460 and diminishing speed ofrotation of sun gear 456 will be a steady reduction in the resultantspeed of rotation of ring gear 458 and so of shaft 446. A state will bereached, before the traction roller axles reach the opposite extreme oftheir angle, in which the speeds of rotation of pinion carrier 460 andsun gear 456 are such that the resultant speed of ring gear 458 and IVToutput shaft 446 is zero and a condition known in the art as “gearedneutral point (GNP)” is attained. In FIG. 22, the GNP is attained whenthe traction roller axles reach their angle in which a value of CVTratio is i_(cg). If the traction roller axles move toward and finallyreach their extreme illustrated in FIG. 21, the speed of rotation of sungear 456 continues to fall while that of rotation of pinion carrier 460remains unchanged, and the ring gear 458 and IVT output shaft 446accordingly rotate with increasing speed in the opposite direction, thatis to say forward direction.

[0197] If the clutch 454 is disengaged and clutch 452 is engaged, thenalthough sun gear 456 remains driven, pinion carrier 460 is freed fromrestraint and the sun gear 456 therefore transmits no drive. The IVToutput shaft 446 is driven solely from the output discs 50, 52 by thechain 462. As is well known in the art, by appropriate choice of gearingand CVT ratios, it is possible to ensure that when the engagement ofclutches 454 and 452 is reversed at the end of a period of operation infirst regime, when the traction roller axles are in their illustratedpositions in FIG. 21 and the IVT output shaft 446 is therefore rotatingat the maximum forward speed of which it is capable in the first regime,the instantaneous forward speed at which the IVT output shaft 446 isdriven as the second regime takes over is exactly the same. Such achange of regimes, resulting in no instantaneous change of IVT outputshaft speed, is known as a “synchronous point” (see FIG. 22). If,following the adoption of second regime, the inclination of the tractionroller axles is once again progressively changed, this time back towardsthe high position, the forward speed of the IVT output shaft 446 risesprogressively to its maximum value.

[0198] In the embodiment, the present invention is implemented by usingthe above-mentioned value i_(cg) of CVT ratio as the precision requiredvalue of CVT ratio. This embodiment is substantially the same as thepreviously described embodiments except the above-mentioned point. Byholding the CVT ratio at the value i_(cg) with excellent precision, zerospeed of the IVT output shaft 446 at the GNP is maintained, enhancingcontrol quality of the IVT.

[0199] This section provides description on the manner of determiningthe width d of a dead zone. The width d is defined as the double ofe_(d) (d=2×e_(d)) and must satisfy the following relationship.

d≧A+m  (28)

[0200] where: A is the magnitude of noise and expressed as 2×(amplitudeof noise), that is, 2×(i_(cp)α₁+i_(cp)α₂);

[0201] m is the sum of minimum interval in CVT ratio that can beattained by the actuator (stepper motor) 188 and minimum interval in CVTratio that can be measured by the measured CVT ratio generator 340.

[0202] The width d_(min) of dead zone that can be narrowed at the filterand command generator manager 352 may be defined as:

d _(min) =A _(min) +m  (29)

[0203] where: A_(min) is minimum width of noise resulting fromprocessing at the filter 348.

[0204] With reference to FIG. 23, the cases 1 and 2 are illustrated. InFIG. 23, it is assumed that the adjacent two of CVT ratios G_(n−1),G_(n), G_(n+1), . . . are equidistant at minimum interval ΔG that can beattained by the stepper motor 188. In the case 1, the width d₁ of deadzone (d₁=2×e_(d1)) about a desired value of CVT ratio is narrower thanthe interval ΔG. In the case 2, the width d₂ of dead zone (d₂=2×e_(d2))about a desired value of CVT ratio is wider than the interval ΔG.

[0205] Assume that the current value of CVT ratio is G_(n+1), a desiredvalue of CVT ratio is between the values G_(n+1) and G_(n), and adeviation e₀ exists.

[0206] In the case 1, a shift to the value G_(n) of CVT ratio takesplace, remaining a deviation e₀₁ that is greater than e_(d1), causing ashift back to the original value G_(n+1). The hunting therefore takesplace.

[0207] In the case 2, a shift to the value G_(n) of CVT ratio takesplace, remaining a deviation e₀₁. Since this deviation e₀₁ does notexceed e_(d2), the CVT ratio stays at the value G_(n). There is nohinting.

[0208] From the preceding description on FIG. 23, it will be understoodthat the width d of dead zone should exceed the minimum interval ΔG forprevention of hunting. In practical application, however, an errorinherently occur during operation at the measure CVT ratio generator 340(see FIG. 4) and noise that remains after filtering at the filter 348must be taken into account. Minimum magnitude of such noises needs to beadded to the minimum interval in CVT ratio that can be attained by thestepper motor 188 in determining the width of dead zone.

[0209] The simulation results of FIGS. 24A, 24B and 24C clearly tellthat the embodiments of the present invention provide enhanced CVT ratiocontrol in attaining a precision required value i_(cl) of CVT ratio withexcellent precision without hunting and standing deviation.

[0210] With reference to FIG. 24A, upon determination that a desiredvalue of CVT ratio had been accomplished after the desired value of CVTratio had matched with the precision required value i_(cl) of CVT ratio,dead zone was narrowed and filter gains were lowered. This simulationresult clearly shows the effectiveness of the embodiments of the presentinvention.

[0211] With reference to FIG. 24B, upon determination that a desiredvalue of CVT ratio had been accomplished after the desired value of CVTratio had matched with the precision required value i_(cl) of CVT ratio,dead zone was narrowed without lowering filter gains. This simulationresult clearly shows the occurrence of hunting.

[0212] With reference to FIG. 24C, upon determination that a desiredvalue of CVT ratio had been accomplished after the desired value of CVTratio had matched with the precision required value i_(cl) of CVT ratio,without narrowing dead zone, filter gains were lowered. This simulationresult clearly shows the occurrence of standing deviation.

[0213]FIG. 25 clearly shows the relationship between control gain anddead zone. It will be understood that if dead zone is narrowed, thecontrol gain is applied to deviation between estimated value i_(c) anddesired value i_(c)* over range of smaller values, so that the precisionrequired value of CVT ratio can be attained with excellent precisionwhile suppressing vibrations.

[0214] While the present invention has been particularly described, inconjunction with exemplary embodiments, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

[0215] This application claims the priority of Japanese PatentApplication No. P2001-369913, filed Dec. 4, 2001, the disclosure ofwhich is hereby incorporated by reference in its entirety.

What is claimed is:
 1. A system for enhanced ratio control in acontinuously variable transmission (CVT) including a ratio controlelement positionable by an actuator in response to an actuator commandto establish various CVT ratios in the CVT, the system comprising: ameasured CVT ratio generator obtaining information of an actual CVTratio established in the CVT to give a measured value of CVT ratio; afilter processing the measured value of CVT ratio in a manner to refinethe information of the actual CVT ratio to give an estimated value ofCVT ratio; a command generator determining the actuator command suchthat the actuator command remains unaltered when a deviation of theestimated value of CVT ratio from a desired value of CVT ratio stayswithin a dead zone; and a filter and command generator manager narrowingthe dead zone to meet precision requirement upon determination that thedesired value of CVT ratio has been accomplished and adjusting thefilter to gain requirement for keeping the magnitude of signal atfrequency of noise within the narrowed dead zone.
 2. The system asclaimed in claim 1, further comprising: a noise estimator determiningamplitude and frequency of noise contained in the measured value of CVTratio, and wherein the filter and command generator manager determinesthe filter gain based on the estimated amplitude at the estimatedfrequency of noise and the dead zone.
 3. The system as claimed in claim2, further comprising a desired CVT ratio generator generating thedesired value of CVT ratio in response to a vehicle speed indicative ofspeed of rotation of an output member of the CVT and operator torquedemand.
 4. The system as claimed in claim 3, wherein, upon determinationthat the desired value of CVT ratio has been accomplished when theprecision requirement is present, the filter and command generatormanager provides the narrowed dead zone, which is narrower than deadzone provided upon determination that the desired value of CVT ratio hasbeen accomplished when the precision requirement is absent.
 5. Thesystem as claimed in claim 4, wherein the filter and command generatormanager determines the filter gain so as to suppress the amplitude ofnoise below a value resulting from subtracting from the width of thenarrowed dead zone a sum of minimum interval in CVT ratio that can beattained by the actuator and minimum interval in CVT ratio that can bemeasured by the measured CVT ratio generator.
 6. The system as claimedin claim 4, wherein the dead zone is greater in width than a sum ofminimum interval in CVT ratio that can be attained by the actuator,minimum interval in CVT ratio that can be measured by the measured CVTratio generator, and minimum amplitude of noise.
 7. The system asclaimed in claim 4, wherein the narrower the dead zone, the lower thegain at frequency of noise.
 8. The system as claimed in claim 4, whereinthe at least one sensor includes an input speed sensor generating afirst train of pulses indicative of speed of rotation of an input memberof the CVT and an output speed sensor generating a second train ofpulses indicative of speed of rotation of an output member of the CVT;wherein the filter includes a low pass filter; wherein the measured CVTratio generator gives, as the measured value of CVT ratio, a ratiobetween speed of rotation of the input member and speed of rotation ofthe output member, which speeds are determined based on frequency of thefirst train of pluses and frequency of the second train of pulses,respectively; and wherein the filter gain at frequency of noise is lowerduring operation with CVT ratios used at low speeds of rotation of theoutput member than it is during operation with CVT ratios used at highspeeds of rotation of the output member.
 9. The system as claimed inclaim 4, wherein the at least one sensor includes an input speed sensorgenerating a first train of pulses indicative of speed of rotation of aninput member of the CVT and an output speed sensor generating a secondtrain of pulses indicative of speed of rotation of an output member ofthe CVT; wherein the filter includes a band reject filter; wherein themeasured CVT ratio generator gives, as the measured value of CVT ratio,a ratio between speed of rotation of the input member and speed ofrotation of the output member, which speeds are determined based onfrequency of the first train of pluses and frequency of the second trainof pulses, respectively; and wherein the lower the speed of rotation ofone of the input and output members of the CVT, the lower the frequencyto be cut off at the band reject filter.
 10. The system as claimed inclaim 4, wherein the precision requirement is present when the desiredvalue of CVT ratio has accomplished one of the largest CVT ratio and thesmallest CVT ratio.
 11. The system as claimed in claim 4, wherein theCVT is an infinitely variable transmission (IVT) having a geared neutralpoint (GNP), and wherein there is the requirement for precision inholding a predetermined value of CVT ratio needed accomplish the GNP.12. The system as claimed in claim 4, wherein the filter includes anobserver that receives, as inputs, the actuator command as well as themeasured value of CVT ratio to provide the estimated value of CVT ratio.13. The system as claimed in claim 1, wherein the filter and commandgenerator manager increases control gain used in determining theactuator command at the command generator after narrowing the dead zone.14. A method for enhanced ratio control in a continuously variabletransmission (CVT) including a ratio control element positionable by anactuator in response to an actuator command to establish various CVTratios in the CVT, the method comprising: obtaining information of anactual CVT ratio established in the CVT to give a measured value of CVTratio; processing the measured value of CVT ratio in a manner to refinethe information of the actual CVT ratio to give an estimated value ofCVT ratio; determining the actuator command such that the actuatorcommand remains unaltered when a deviation of the estimated value of CVTratio from a desired value of CVT ratio stays within a dead zone; andnarrowing the dead zone to meet precision requirement upon determinationthat the desired value of CVT ratio has been accomplished and adjustingthe filter to gain requirement for keeping the magnitude of signal atfrequency of noise within the narrowed dead zone.
 15. The method asclaimed in claim 14, further comprising determining amplitude andfrequency of noise that may be contained in the measured value of CVTratio, and wherein the processing the measured value of CVT ratioincludes determining filter gain based on the amplitude at the frequencyof noise and the dead zone.
 16. The method as claimed in claim 15,wherein the precision requirement is present when the desired value ofCVT ratio matches with a precision required value of CVT ratio.
 17. Themethod as claimed in claim 16, wherein the precision requirement isabsent when the desired value of CVT ratio fails to match with theprecision required value of CVT ratio.
 18. The method as claimed inclaim 17, wherein the precision required value of CVT ratio is thelargest CVT ratio.
 19. The method as claimed in claim 18, wherein theprecision required value of CVT ratio is the smallest CVT ratio.
 20. Themethod as claimed in claim 17, wherein the narrowed dead zone isprovided upon determination that the desired value of CVT ratio has beenaccomplished when the desired value of CVT ratio and the precisionrequired value of CVT ratio match with each other, and the narrowed deadzone is narrower than dead zone provided upon determination that thedesired value of CVT ratio has been accomplished when the desired valueof CVT ratio and the precision required value of CVT ratio fail to matchwith each other.
 21. A system for enhanced ratio control in acontinuously variable transmission (CVT) including a ratio controlelement positionable by an actuator in response to an actuator commandto establish various CVT ratios in the CVT, the system comprising:sensor means for generating a train of pulses indicative of speed ofrotation of a predetermined rotary member of the CVT; means for derivinginformation of an actual CVT ratio established in the CVT out of atleast the train of pulses to give a measured value of CVT ratio; filtermeans for processing the measured value of CVT ratio in a manner torefine the information of the actual CVT ratio to give an estimatedvalue of CVT ratio; means for determining the actuator command such thatthe actuator command remains unaltered when a deviation of the estimatedvalue of CVT ratio from a desired value of CVT ratio stays within a deadzone; means for narrowing the dead zone to meet precision requirementupon determination that the desired value of CVT ratio has beenaccomplished; and adjusting filter gain at the filter means in a mannerto keep amplitude at frequency of noise within the narrowed dead zone.22. A computer readable storage medium having stored thereon dataindicative of instructions readable by a microprocessor for carrying outenhanced ratio control in a continuously variable transmission (CVT),the CVT including a ratio control element positionable by an actuator inresponse to an actuator command to establish various CVT ratios in theCVT, the computer readable storage medium comprising: instructions forobtaining information of an actual CVT ratio established in the CVT togive a measured value of CVT ratio; instructions for processing themeasured value of CVT ratio in a manner to refine the information of theactual CVT ratio to give an estimated value of CVT ratio; instructionsfor determining the actuator command such that the actuator commandremains unaltered when a deviation of the estimated value of CVT ratiofrom a desired value of CVT ratio stays within a dead zone; andinstructions for narrowing the dead zone to meet precision requirementupon determination that the desired value of CVT ratio has beenaccomplished and adjusting the filter to gain requirement for keepingthe magnitude of signal at frequency of noise within the narrowed deadzone.